Truck marker light

ABSTRACT

A marker or clearance light for semi trailers and the like which increases the life by a factor of from 3 to 10.

This application is a continuation in part of application Ser. No.742,200 filed Nov. 16, 1976, now U.S. Pat. No. 4,128,860.

By law semi trailers are required to have marker lights outlining thebody. Under normal conditions the lights have a life of about 300 hours.When a light goes out, it must be replaced and the cost of replacementexceeds the cost of the light. Lights with two lamps have been proposedon the theory that both lamps will not burn out at the same time. Thishas made a very small improvement. When one lamp burns out, the otherlamp is almost ready to go so the actual increase in life is only about50 hours. It is cheaper to replace the entire unit when one lamp burnsout rather than to take the risk of a high cost on-the-road replacement.The problem of marker lights has existed for a long time.

This invention is a dual lamp unit which makes a three to ten foldincrease in life by a structure for absorbing vibration and for burningthe lamps in sequence. Lamp filaments become brittle in use but unburnedlamps remain ductile and are not affected by vibration. When applicant'ssecond lamp is switched on, it has a filament in the same condition as abrand new lamp so that double life can be expected. However thevibration absorbing characteristics of the switching structure stillfurther increase the life so that the life is increased by a factor offrom 3 to 10. Instead of a life of from 300 to 350 hours, applicant getsa life of from 1000 to 3000 or 3500 hours. The unit works equally wellwith positive and negative ground electrical systems, an importantfeature since trucks are about equally divided between positive andnegative ground systems.

In the drawing FIG. 1 is a top plan view of a preferred form of markerlight with the lens removed,

FIG. 2 is a section of line 2--2 of FIG. 1 with the lens in place,

FIG. 3 is a bottom plan view of the printed circuit board carrying thelamps and the circuit connections,

FIG. 4 is a circuit diagram,

FIG. 5 is a section through one of the supports for the printed circuitboard,

FIG. 6 is a section of the lens mounting.

The light has a plastic base 1 with mounting holes 2 and 2a at oppositeends for screws for attachment to a trailer body or frame. A groundstrap 3 has an eyelet 4 in the hole 2a. Around the periphery of the baseis an upstanding rim 5 having a bead 6 at its upper edge which makes aweathertight fit with the rim 7 of a lens 8. As shown in FIG. 6 the bead6 and rim 7 have interengaging cam surfaces 6a, 7a which hold the rim 7tight against a shoulder 7b on the base and prevents removal of the lensunder shocks and vibrations encountered in service. The weatherresistant plastic used for the lens and base are sufficiently yieldableto allow the lens to be pried off the base by a screwdriver insertedinto one of the notched 7c in the shoulder 7b. On the bottom wall of thebase are integral unstanding studs 9 having shoulders 10 for supportinga printed circuit board 11 in the optically required relation to thelens 8. The printed circuit board is fastened to the base by projections12 on the studs which extend through and have an interference fit inrubber grommets 13a in mounting holes 13. When the board grommets 13aare seated on the shoulders 10 the interference fit produces a grip onthe projections 12 tight enough to prevent unwanted removal duringservice. Enlarged heads 12a assist in preventing removal of the board.

On the upper side of the printed circuit board 11 is a socket 15 for adual filament lamp 17, 18. The dual filament lamp is electricallyequivalent to two separate lamps. The lamp filament 17 is supplied bycurrent through conductors 15a, 15b. The lamp filament 18 is supplied byconductors 16a, 16b.

The power to the lamp filaments is fed through a full wave bridgerectifier 19 consisting of rectifier elements 19a, 19b, 19c, 19d and asolid state switching circuit consisting of trandistors 20, 21 and aresistor 23 connected across the output of rectifier 19 as shown inFIGS. 3 and 4. The rectifier 19 has input terminals 19e and 19fconnected to power input terminal 22 and ground terminal 24 and outputterminal 19g connected to lamp filament terminals 15b and 16b and outputterminal 19h connected to transistor emitter electrodes 20e and 21e.Resistor 23 has leads 23a and 23b connected respectively to therectifier output terminals 19g and to transistor electrodes 20c and 21b.For trucks with negative ground, the power input terminal 22 is positivewith respect to ground 24 and current for the lamp filament 17 flowsthrough rectifier 19a to the lamp and from the lamp through base andemitter electrodes 20b and 20 e of transistor 20 and through rectifier19b to ground. For trucks with positive ground, ground is positive withrespect to power input terminal 22, and current flows from groundthrough rectifier 19c to the lamp filament 17 from the lamp 17 throughbase and emitter electrodes 20b and 20e of transistor 20 and throughrectifier 19d to the terminal 22.

When the marker light is first installed, current is compelled to flowthrough lamp filament 17 because transistor 21 is biased off byconnection of collector electrode 20c of transistor 20 to the baseelectrode 21b of transistor 21. When the lamp filament 17 burns out thevoltage from resistor 23 biases the base electrode of transistor 21 onand causes the flow of current to immediately switch to lamp filament 18and to flow through the collector electrode 21c and emitter electrode21e either to ground 24 through rectifier 19b when terminal 22 ispositive or to terminal 22 through rectifier 19d when terminal 22 isnegative. While both lamp filaments 17, 18 are subject to shock andvibrations incident to the use of the truck, the lamp filament 18 is notaffected while the lamp 17 is lighted. The solid state switching meansand the other parts carried by the board 13 are so rugged as to beinsensitive to shocks and vibration. As manufactured, the lamp filaments17 and 18 are ductile. Embrittlement starts the moment a lamp is lightedand progresses until the filament breaks. When the lamp filament 18 isswitched on, it has a life expectancy equal to lamp 17. The result isthat the life of the marker light is substantially doubled. Since thecost of replacing a single lamp on the road greatly exceeds the cost ofthe entire marker light, doubling the life is very important. In mostcases, the subject marker light will not require any lamp replacementbetween major overhauls when the truck or trailer is returned to theshop for extensive rebuilding.

The printed circuit board 11 and the supporting grommets still furtherincrease the lamp filament life by reducing the transmission ofvibrations in accordance with the formula P=103.254--(0.420/_(S)) whereP=% reduction in transmission of vibration and S = static deflection ininches of the grommets under the weight of the printed circuit board andthe lamp carried thereby. For a static deflection of 0.01 inches, thepercentage reduction is 60% and the effect of the 60% of reduction is toincrease the filament life up to 500%. A static deflection of 0.01inches does not significantly change the relation of the lamps to thelens 8 and therefore has negligible effect on the photometricmeasurements of light intensity from the light.

The light can be used interchangeably with all existing marker lightswithout regard to the polarity of the electrical system and willincrease the service life by a factor of 3.5 to 10, a major improvement.

The printed circuit board 13 when solidly mounted on parts 9 without thegrommet increases the service of each lamp from 25--30%. The glass fiberepoxy or equivalent board material required to prevent water absorptionhas inherent vibration and shock isolation properties which help protectthe lamp filaments. If the mounting 13a were omitted the service life ofthe marker light would be increased by a factor of from 2 to 2.5.

I claim:
 1. A marker light for trucks, semi-trailers and the like havingelectrical systems with either positive or negative ground comprising abase having means for mounting the same on a truck, a lens mounted onthe base, lamp means having first and second filaments, lamp supportingmeans, means for mounting the lamp supporting means on the base, saidlamp supporting means having means for receiving said lamp means, aground terminal adapted to be connected to the truck electrical systemground, a power terminal adapted to be connected to the live terminal ofthe truck electrical system, a first transistor, a second transistor, afull wave bridge rectifier having its input connected across said powerand ground terminals and having its output connected in series throughthe base and emitter of said first transistor to the first filament andalso having its output connected in series through the collector andemitter of said second transistor to the second filament, a connectionfrom the collector of the first transistor to the base of the secondtransistor for biasing the second transistor off only while the firsttransistor is on and current is flowing throught the first transistor aswould be the case when the first filament is unbroken, and a biasresistor connected to the base of the second transistor for biasing saidsecond transistor on, the bias from said resistor being overcome by thebias from said first transistor when said first transistor is on andconducting current through the first filament.
 2. The light of claim 1in which the means for mounting the lamp supporting means is furtherdefined as rubber mountings.
 3. The light of claim 1 in which the lampsupporting means is further defined as a printed circuit board havingrubber grommets in supporting relation between it and the base.